Quote Originally Posted by tekjunkie View Post
I will try to explain. As Everybody has stated, the Intel specs say that quads have a reference GTL of 66.7% or 67%(hence the 0.667 or 0.67) of VTT/vFSB. But for some reason, even if the board gives the GTL voltages as per Intel's reference numbers, the chips are not stable.I don't want to go into "Who's fault is it anyway?" game between the mobo manufacturers or Intel. Remember, this only happens @ high FSBs with the quad.So to make the chips to be stable you think it's the Vcore and increase the Vcore, but still end up with an unstable chip and also unnecessary heat. That's the reason a lot of us with our experience with playing around with GTLs can give you a reference point like saying the 45nm quads seem to be stable with less of a GTL than the refernce of 67% of VTT.

Now, going into the calculation, let's say your rig is semi stable with a VTT of 1.30V. According to the reference from Intel, if you leave the GTLs @ auto, it will give the GTLs exactly that(0.667 times 1.3). But, for 45nms you want your GTLs lower than that. So you determine that you have to give negative values for the GTL so that board will give 0.667 times VTT-xx where -xx is the amount that you actually set in the BIOS of different boards. That's why when you see in my spreadsheet, I had put Auto as zero. Now the question is what does the -xx amount that you would have to specify in the BIOS. It's a simple math calculation. If you want to give a GTL of say 0.657, you are reducing the reference GTL by -0.01. So for a VTT of 1.30V, the equation becomes 1.3x-0.01x1000 = -13mV. The x1000 is because it's in milli volts.For a GTL for 0.647, you go 1.3x-0.02x1000 and so on and so forth.


Sorry about the long post. Hope this helps.
The thing is boards do not give just 0.667x for all GTL Ref's when left on auto. They give 0.635x for GTL Ref (0/2) and 0.667x for GTL Ref (1/3).

There are a few mathematical ways of working this out, just do whatever works for you. Your equation is fine. I gave the equation in the format in the first post as that is what is given in some bioses. When you just have the multipliers (0.635x, 0.667x etc), just choose whichever one you want and you're done.

This is a hard thing to explain, understanding how AGTL+ signals work can be tricky, but tuning them is the easy part, but for an inexperienced overclocker, it is something best left alone. To understand them properly you just need to do a bit of reading first.

In most cases for average overclocks, you are fine to just leave them on auto, and as always, if you don't understand what a setting in your BIOS means, don't touch it.